bug#21846: 25.0.50; emacs hebrew script bidi nikud rendering bug

[Wolfgang Jenkner]

On Sun, Jan 03 2016, K. Handa wrote:

> I committed changes to enable ftfont-base font-backend to handle wider
> range of combining characters for non-OTF fonts.  So, hebrew
> diacticicals should be rendered by "Aharoni CLM" font.
>
> Could you verify it?

These changes (536f48e, 9835757, resp. the backports to emacs-25, viz.
4a3db0f, ad879b7) seem to break rendering of some Indic scripts.
Conjuncts are not composed anymore but rendered with virāma instead.
E.g., please see the Hindi entry of the HELLO file.

Apparently, the reason is this change

-      if (0x300 <= c1 && c1 <= 0x36F)
+      if (CHAR_HAS_CATEGORY (c1, '^'))

as, say, "DEVANAGARI SIGN VIRAMA" is excluded by the old condition but
included by the new one:

(category-set-mnemonics (char-category-set ?\u094d))
=> "^i"